Variable response time transient partial flow sampling system and method

Abstract

A partial flow dilution tunnel in a gas sampling system is connected to the exhaust from an internal combustion engine. More accurate gas sampling results are enabled for accounting for a delay from when the engine produces an exhaust change to when that transient arrives at a probe location. Thus, an estimated time delay is determined, and the gas sampling system is operated at least in part based upon that estimated time delay for the exhaust to arrive at the sampling location.

1. A method of operating a partial gas sampling system, comprising the steps of:
 estimating a time delay for exhaust to arrive at a sampling area of an exhaust stack; 
 setting a proportion of dilution to exhaust sample for the partial gas sampling system at least partially based upon the estimated time delay. 
 
     
     
       2. The method of  claim 1  including changing an air dilution flow rate in response to a change in mass flow of exhaust in the exhaust stack. 
     
     
       3. The method of  claim 2  wherein the estimating step includes a step of determining an exhaust stack volume. 
     
     
       4. The method of  claim 3  wherein the estimating step includes a step of determining an exhaust temperature; and
 determining an exhaust volumetric flow rate based at least in part on the determined exhaust temperature. 
 
     
     
       5. The method of  claim 4  wherein the estimating step includes a step of determining an exhaust pressure; and
 determining the exhaust volumetric flow rate based at least in part on the determined exhaust pressure. 
 
     
     
       6. The method of  claim 5  including a step of determining an expected time for a portion of exhaust to arrive at a predetermined location in the exhaust stack based at least in part on the estimated time delay; and
 determining an actual arrival time at the predetermined location. 
 
     
     
       7. The method of  claim 6  including a step of comparing the actual arrival time to the expected arrival time; and
 adjusting the estimated time delay based at least in part on the comparison. 
 
     
     
       8. The method of  claim 2  including a step of determining an expected time for a portion of exhaust to arrive at a predetermined location in the exhaust stack based at least in part on the estimated time delay; and
 determining an actual arrival time at the predetermined location. 
 
     
     
       9. The method of  claim 8  including a step of comparing the actual arrival time to the expected arrival time; and
 adjusting the estimated time delay based at least in part on the comparison. 
 
     
     
       10. The method of  claim 1  including the step of detecting an engine transient; and
 changing a dilution air flow rate at a time corresponding to the estimated time delay for the engine transient. 
 
     
     
       11. The method of  claim 1  comprising the step of disconnecting one of a large engine and a small engine from the exhaust stack; and
 connecting an other of the large engine and the small engine to the exhaust stack. 
 
     
     
       12. A gas sampling system comprising:
 an exhaust stack section; 
 a dilution sampling probe positioned in the exhaust stack section; 
 a controller operably coupled to control a proportionality of dilution to exhaust sample; and 
 a computer in control communication with the controller, and including a control algorithm that includes a time delay estimation algorithm operable to determine a delay time for exhaust to arrive at the dilution sampling probe. 
 
     
     
       13. The gas sampling system of  claim 12  including a temperature sensor operably coupled to sense temperature in the exhaust stack section, and being in communication with the computer. 
     
     
       14. The gas sampling system of  claim 13  including a pressure sensor operably coupled to sense a pressure in the exhaust stack section, and being in communication with the computer. 
     
     
       15. The gas sampling system of  claim 12  including a transient sensor positioned in the exhaust stack, and being in communication with the computer. 
     
     
       16. The gas sampling system of  claim 12  wherein the controller includes means for adjusting a dilution air flow rate. 
     
     
       17. A gas sampling system comprising:
 an exhaust stack section; 
 a sampling probe positioned in the exhaust stack section; 
 a controller operably coupled to control a proportionality of dilution to exhaust sample; 
 a computer in control communication with the controller, and including a control algorithm that includes a time delay estimation algorithm operable to determine a delay time for exhaust to arrive at the sampling probe; and 
 the control algorithm includes means for determining an exhaust volumetric flow rate. 
 
     
     
       18. A gas sampling system comprising:
 an exhaust stack section; 
 a sampling probe positioned in the exhaust stack section; 
 a controller operably coupled to control a proportionality of dilution to exhaust sample; 
 a computer in control communication with the controller, and including a control algorithm that includes a time delay estimation algorithm operable to determine a delay time for exhaust to arrive at the sampling probe; 
 a transient sensor positioned in the exhaust stack, and being in communication with the computer; and 
 the control algorithm includes a time delay estimation adjustment algorithm operable to compare an estimated time delay to a sensed time delay for an exhaust transient to arrive at the transient sensor. 
 
     
     
       19. The gas sampling system of  claim 18  wherein the transient sensor includes a NOx sensor. 
     
     
       20. The gas sampling system of  claim 19  including a temperature sensor operably coupled to sense temperature in the exhaust stack section, and being in communication with the computer.